Determination of water permeability for cementitious materials with minimized batch effect Zhidong Zhang, George Scherer Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA Abstract Values of water permeability for cementitious materials reported in the literature show a large scatter. This is partially attributed to the fact that materials used in different studies are different. To eliminate the effects of cements, specimen preparation, curing conditions and other batch effects, this study employs a long cylindrical cement paste to prepare all speci- mens for a variety of permeability determination methods, such as beam bending, sorptivity, Katz–Thompson and Kozeny-Carman equations. Permeabilities determined by these methods are then used in a moisture transport model. Compared with the measured mass loss curves, we found that permeability determined by the beam bending method provides much closer re- sults to the measured ones than other methods. The difference results from that the saturated specimen is used in the beam bending method while specimens in other methods are dried (or rewetted). As already shown in the literature, the microstructure of the dried or rewet- ted specimens is altered and different to the original microstructure of the water saturated specimens. ... 1 Introduction The durability of concrete structures is always closely related to the moisture transport properties in cementitious materials. The liquid uptake when concrete is in contact with liquid water (e.g., groundwater, rain) can induce the penetration of aggressive agents (e.g., chloride ions) through the concrete cover. A common natural condition - drying/wetting cycles - can increase the rate of chloride ingress compared to the saturated condition [1]. Carbon dioxide may transport within the gaseous phase in concrete and decrease pH of the pore solution. All these processes are able to result in corrosion to the rebars and deterioration of concrete. For this reason, moisture transport becomes a crucial theme when evaluating the durability. Moisture transport in partially saturated porous media such as cementitious materials is mainly governed by the transport of three phases: liquid water, water vapour and dry air. The previous studies have shown that dry air has very low contribution to the mass of moisture transport and only causes fluctuating air pressure in the material [2, 3]. This conclusion was also drawn by the asymptotic analysis performed by Coussy and Thi´ ery [4, 5]. In addition, considering that the liquid phase remains incompressible and total gas pressure is constant, the mass balance equations of moisture transport can be represented by a simplified equation, including only liquid water and vapour [6, 7]. Mainguy et al. [2] further simplified the model for specific conditions, by considering only liquid water and neglecting the vapour diffusion. They found that such a model can give results for simulating drying mass loss curves very similar to the multiphase model. Hence, the 1 arXiv:1810.06463v1 [physics.app-ph] 4 Sep 2018
Determination of water permeability for cementitious materials with minimized batch effect
Apr 29, 2023
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